The present invention relates generally to lasers and in particular to controlling fiber coupling between an array of lasers and an optical output.
Fiber coupling is often an essential but costly step in packaging various waveguide devices for telecommunication applications. On account of the very small optical modes in single mode waveguide devices, very tight submicron tolerances are often required in the packaging.
Generally, the devices are actively aligned. For example to fiber couple a telecommunication laser, the device is activated, and the optical power coupled to the fiber is monitored as the positions of the various optical elements in the package are varied. When the coupling is maximized, the optical elements are permanently fixed in position. The process is time consuming, costly, and often not very reproducible due to contraction in epoxies or thermal expansion of the components.
Furthermore, all the components in the package should be made absolutely immobile for the above procedure to maintain effectiveness over time. Any change in the position of the elements decreases the optical coupling. This makes hybrid integration of components with varying expansion coefficients very difficult. For example, to package a laser with a lithium niobate modulator, the laser uses hard solder for thermal heatsinking, while the modulator uses a soft epoxy that does not stress the crystal. The relative position of these devices will vary in the package due to the mismatch in the materials. Similarly, solders and epoxies tend to cause stress in the fiber, which affects yield and reliability and can cause birefringence in the fiber that influences the polarization of light in the core.
The present invention provides adjustable optical coupling systems and methods. In one embodiment, a laser from an array of lasers is selected in which each laser emits light at different wavelengths. An optical path from the laser to an optical output is established such that light from the laser is transmitted into an optical output. The optical path established is adjusted to maximize output power of the emitted light into the optical output. In one aspect of the invention, a look-up table is established where the table has entries in which individual lasers in the laser array are each assigned an output power value and an entry in the look-up table that corresponds to the selected laser is identified. In another aspect of the invention, a look-up table is established where the table has entries in which individual lasers in the laser array are each assigned a predetermined output power value and associated with a predetermined location identified for the optical element. An entry in the look-up table that corresponds to the selected laser is identified.
In one embodiment, the system comprises an array of lasers, at least one optical element and an optical output such that light from a laser from the array of lasers is directed into the optical output by the at least one optical element. A controller is also coupled to the at least one optical element and configured to adjust the optical element to maximize output power of the light directed into the optical output. In one aspect of the invention, the system also comprises a plurality of photodetectors proximate the optical output. The controller is coupled to the plurality of photodetectors and is configured to adjust the optical element based on the information provided by the photodetectors. The information provided by the photodetector comprises optical output power of light received at one or more of the photodetector and/or a location of light incident upon one or more of the photodetectors. In another aspect of the invention, the controller generates an error signal to adjust the optical element.
In a further embodiment, the system comprises an array of lasers having lasers configured to emit light, an optical output configured to receive light and a detector near the optical output. The system also includes at least one optical element configured to receive light from a laser from the array of lasers and to direct a portion of the light to the optical output and a portion of light to the detector. A controller is coupled to the at least one optical element and configured to adjust the at least one optical element to maximize output power of the light directed into the optical output. In one aspect of the invention, the optical element comprises a beam splitter and/or a mirror.
In a further embodiment of the invention, the system commprises an array of lasers comprising a first laser and a second laser where the first laser is configured to emit light and the second laser is configured to emit light. An optical output is also provided and configured to receive light from the first laser. The detector near the optical output is configured to receive light from the second laser. Also, at least one optical element is provided and configured to receive light from the first and second lasers and a controller is coupled to the at least one optical element and configured to adjust the at least one optical element to maximize output power of the light into the optical output. In other aspects of the invention, the second laser is a predetermined distance from the first laser.
In another embodiment of the present invention, the system comprises emitting means for emitting light having differing wavelengths, output means, and optical means for directing light having a particular wavelength from the emitting means into the output means. Coupled to the optical means is control means that also adjusts the optical means to maximize power of the light directed into the output means. In another aspect of the invention, the system further comprises reflective means for reflecting light from the emitting means and directed to the output means. In another aspect of the invention, the system provides sensing means for sensing light and is proximate the output means. The control means is coupled to the sensning means and adjusts the optical means based on light sensed by the sensing means.